Frist Check on the title of the seller and clear passage of title. Check since how many years the seller of the revenue site is in possession. Obtain Encumbance Certificate to find any encumbrances are there. Find whether taxes are paid uptodate under Self Assesment Scheme. Check whether owner is residing in the house and the Electricity/water connections are in his name. Revenue sites within the BBMP Limits are being registered in case SAS taxes are paid and Form-B Khata extract is furnished. Approaching an advocate with property papers for opinion on tile will help.
As far as the risks involved are concerned:
* you may have to pay betterment charges and any penalty that may be imposed on building violations or any cess/tax/penalty/charges that may be imposed by the Govt or Local Body (BBMP) for regularisation of revenue sites.
* As far as risks on title and the entitlement of the seller to sell as an absolute owner, it is better to take professional advise personally.